King pin assemblies having rotary kingpins and a swiveling plate to attach the semitrailer to the fifth wheel of a traction vehicle have been known for several years, as evidenced by U.S. Pat. No. 5,411,281. The swiveling of the plate and associated rotation of the kingpin were known to have advantages over non-rotary kingpin assemblies.
Although such assemblies were satisfactory to a certain degree, there remained room for improvement.